Computing \(\mathbb {E}({\tt RV}^4)\) , or equivalently \(\mathbb {E}({\tt CV}^4)\)  is clearly untractable with the former pedestrian approach, and a more systematic strategy is needed. The latter is provided by the work around the orthogonal Weingarten functions [1]}, [2]}, [3]}, [4]}, [5]}, [6]}.
